Dynatron circuit



Jan. 16, 1934. P. o. FARNHAM 1,943,471

DYNATRON CIRCUIT Filed Jan. 15, 1932 Patented Jan. 16, 1934 UNITEDSTATES PATENT ()FFICE DYNATRON CIRCUIT Paul 0. Farnham, Boonton, N. J.,assignor to Radio Frequency Laboratories, Incorporated, Boonton, N. .L,a corporation of New Jersey This invention relates to dynatron circuitsand particularly to methods of and circuits for obtaining. regenerativeamplification.

My copending' application, Ser. No. 563,635, filed SeptemberlS, 1931,describes and claims the method of reflecting a negative capacity intothe input circuit of a dynatron, through a capacitive coupling betweenplate and control grid, by the use ofa plate circuit load which is aresistive impedance for the signal frequencies. According to the presentinvention, a negative resistance is reflected into the input circuit ofa dynatron, through capacitive coupling between the input and outputcircuits by providing a plate circuit load which is capacitive at theradio frequencies.

Objects of the invention are to provide novel methods of andcircuitarrangements for obtaining regeneration in networks including a tubethat is operated as a dynatron, that is, is so energized that it has anegative plate impedance. Further objects are to provide methods of andcircuit arrangements for obtaining substantially constant regenerationover a band of radio frequencies. These and other objects and advantagesof the invention will be apparent from the following specification whentaken with the accompanying drawing,in which V Fig. 1 is a schematicdiagram illustrative of the invention, and

Figs. 2 and 3 are circuit diagrams of embodi- Z9. and the output orplate circuit has a loan Zb, the circuits being coupled by asmallcapacity Cm.

The tube 1 may be of the known screen grid type in which the capacitybetween control grid and plate is of such low magnitude as to prevent aretroactive flow of current from the output to the input circuit.

With the tube 1 operating as a dynatron, the

effect of the coupling capacity Cm is to reflect a negative resistanceinto the tube input circuit so long as the signal frequencies impressedupon the input circuit fall within the range for which the plate load Zbis a capacitive impedance.

In the dynatron detector shown in Fig. 2, the

input circuit of tube 1 may comprise an inductance 2 and adjustablecondenser 3 for tuning the circuit to resonance at a desired signalfrequency. The control grid is coupled to the plate by a small condenserCm which is preferably capable of adjustment but which is not variedduring normal operation of the dynatron detector. The capacity C1 ofabout 15 micromicrofarads represents the inherent capacity between thetube elements, plate and screen. To make the plate load capacitive forsignal frequencies, the composite impedance L, C is arranged betweentheplate and the resistance 4, and a capacity C2 from the junction of L Cand 4 to ground, the values of these impedances being so related thatthe effective impedance of this composite load is capacitive over all ora desired part of the tuning range of the input circuit.

For frequencies of from 550 to 1500 kilocycles, values which satisfythis condition may be:

Resistance 4=100,000 ohms Capacity C: 10 micromicrofarads Capacity C2100 micromicrofarads Inductance L=5 millihenries.

With this circuit arrangement, the eifective capacity of the platecircuit load for radio frequencies varies with frequency in such a waythat the feedback current through the constant capacity Cmmay be made toincrease when the input circuit is tuned to the low frequency end of itsrange. In this way, a falling off of input tuned circuit impedance atlower frequencies rather large capacity, 8, across 4, the externalcircuit from plate to cathode may be made capacitive for the entirerange of signal frequencies. By choosing the values of capacity 5, choke6, and capacity 8 so that this circuit approaches resonance at the lowfrequency end of the range, sufficient increase in feedback currentthrough Cmmay be obtained to give a substantially constant eilect uponthe input circuit when used over the entire radio frequency range.

While the invention provides a simple means for obtaining constantregeneration over a frequency band, it will be apparent that theregeneration may be automatically varied as a function of the frequencyby substituting, for the L, C impedance of Fig. 2, a composite impedancehaving an effective capacity which varies with frequency in any desiredmanner.

The resistance 4 is shown as an illustration of resistance coupling forthe modulation frequency although it will be understood that a choke ortransformer designed to provide coupling for transferring the modulationfrequency output to the succeeding tube may be used in place ofresistance coupling.

While I have described my invention in connection with a tetrodecomprising two grids and a plate, it will be understood that any form ofmultiple-electrode tube, energized in the requisite fashion to reducenegative resistance effects in an internal circuit between one electrodeand the emitter, may be used in applying the principles of my invention.In the appended claims as in the foregoing specification, I employcertain terms, designating the individual electrodes, in accordance withthe following definitions:

Cathode. An electrode thermionic space-current.

Control grid-An electrode so formed and emitting primary positioned inthe tube that its potential with respect to the cathode governs themagnitude of 'the primary thermionic space-current leaving the vicinityof the cathode and available for collection by the remaining electrodes.

Screen-grid.An electrode positively polarized with respect to thecathode and which may serve to accelerate the primary thermionic spacecurrent and/or to provide a return path for secondary spacecurrentsemitted by other electrodes.

Plate.-An electrode positively polarized with respect to the cathode,serving primarily as a collector of primary thermionic space-current andas an emitter of secondary space current. The plate may or may not serveas an output electrode. In the appended claims the term plate thereforedesignates an electrode which forms with the cathode, an internal tubecircuit whose alternating-current resistance is negative within theoperating range.

I claim:

1. Apparatus for producing a negative resistance effect between twoterminals, comprising a vacuum tube and means for impressing on theelements thereof potentials effective to impart a negative plateresistance to said tube, a capacitive load in the plate circuit of saidtube, a capacity coupling the plate and control grid of said tube, aconnection from one of said terminals to the control grid of said tube,and a connection from the other terminal to the cathode of said tube.

2. In a vacuum tube circuit, a tube having the elements thereofsubjected to energizing potentials eifective to impart a negative plateresistance to said tube, and means for establishing a negativeresistance across an external circuit connected between the cathode anda grid element of said tube, said means comprising a plate load having acapacitive impedance at radio frequencies, and a capacitive couplingbetween the tube plate and the grid element.

3. In a detector, a tube subjected to energizing potentials effective togive said tube a negative plate resistance, a circuit tunable over aband of frequencies and connected between the input electrodes of saidtube, an output circuit for said tube having a capacitive impedance forfrequencies within said band, and a capacitive coupling between saidinput and output circuits.

4. In a detector for modulated signals, the combination with a tubehaving a negative internal plate-cathode resistance, an input circuittunable over a band of radio frequencies for said tube, and an outputcircuit including an audio frequency load impedance, of means impartingto the output circuit a load impedance which is capacitive at radiofrequencies, and a capactive coupling between the dynatron plate andcontrol grid.

5. The invention as set forth in claim 4, wherein said means comprises acondenser connected between the plate and said audio frequency loadimpedance, a direct current path shunted across said condenser and acondenser connected across said audio frequency load impedance, saidpath having a high impedance at radio frequencies.

6. The invention as set forth in claim 4, wherein said means includes acapacitive impedance connected between the plate and cathode of saidtube, a radio frequency inductance between the plate and said audiofrequency load, and a condenser across said audio frequency load, saidnetwork of capacities and inductance presenting an eifective capacitiveimpedance to the plate cathode terminals of said tube over the band ofradio frequency.

'7. The invention as set forth in claim 4, wherein the impedance of saidradio frequency load impedance varies with frequency at such rate as tomaintain a substantially constant regenerative effect upon the inputcircuit over its tuning range.

8. In a detector for modulated signals, the combination with a tubehaving a negative internal plate-cathode impedance, an input circuittunable over a band of radio frequencies, and a capacitive couplingbetween the plate and control grid, of an output circuit for said tubesaid output circuit including an audio frequency load and means forproducing a substantially constant regenerative effect through saidcapacity coupling as said input circuit is tuned over said band of radiofrequencies.

9. The invention as set forth in claim 8,

wherein said means comprises a condenser be tween the plate and saidaudio frequency load,

between the plate and said audio frequency load and a condenser acrosssaid audio frequency load.

11. In a transmission system, the combination with a tube having anegative internal plate-cathode resistance, an input control-gridcircuit tunable over a band of radio frequencies, and an output circuitconnected to the plate and including an audio frequency load impedance,of means imparting to the output circuit, an impedance which iscapacitive at radio frequencies, and a capacity coupling between theplate and control grid.

12. In the operation of an electron tube having a cathode, a controlgrid, an input circuit connected to said control grid, a screen grid,-and a plate, the method of introducing negaist with respect to thecathode that the internal circuit between said fourth electrode and saidcathode exhibits a negative alternating current resistance, the methodof introducing negative-resistance into the input circuit whichcomprises including in an external circuit between said fourth electrodeand said cathode a load having a capacitive impedance at the operatingfrequencies, and capacitively coupling said fourth electrode to saidcontrol grid.

PAUL O; FARNHAM.

